1. Field of the Invention
The invention relates to a device for determining the quality of an output signal to be generated by a signal processing circuit with respect to a reference signal, which device is provided with.
a first signal processing arrangement, coupled to the first signal input of the first series circuit, for generating the a first signal parameter as a function of time and frequency, and
a first compressing arrangement, coupled to the first signal processing arrangement, for compressing a first signal parameter and for generating a first compressed signal parameter,
a second series circuit having a second input for receiving the reference signal, which second series circuit is provided with
a second compressing arrangement, coupled to the second input, for generating a second compressed signal parameter,
a combining circuit, coupled to a first output of the first series circuit and to a second output of the second series circuit, for generating a quality signal, which combining circuit is provided with
a differential arrangement, coupled to the two compressing arrangements, for determining a differential signal on the basis of the compressed signal parameters, and
an integrating arrangement, coupled to the differential arrangement, for generating the quality signal by integrating the differential signal with respect to time and frequency,
a scaling circuit which is situated between inputs of both compressing arrangements, which scaling circuit is provided with
a further integrating arrangement for integrating a first series circuit signal and a second series circuit signal with respect to frequency, and
a comparing arrangement, coupled to the further integrating arrangement, for comparing the two integrated series circuit signals and for scaling at least one series circuit signal in response to the comparison.
2. Description of the Prior Art
Such devices are disclosed in WO 96/28953, WO 96/28952 and WO 96/28950, which international patent applications define inventions for improving a known device disclosed in J. Audio Eng. Soc., Vol. 40, No. 12, December 1992, in particular xe2x80x9cA Perceptual Audio Quality Measure Based on a Psychoacoustic Sound Representationxe2x80x9d by John G. Beerends and Jan A. Stemerdink, pages 963-978 (hereinafter xe2x80x9cthe Beerends et al paperxe2x80x9d), more particularly FIG. 7. The device described in WO 96/28953 determines the quality of an output signal to be generated by a signal processing circuit, such as, for example, a coder/decoder, or codec, with respect to a reference signal. The reference signal is, for example, an input signal to be presented to the signal processing circuit, although the possibilities also include using, as the reference signal, a pre-calculated ideal version of the output signal. The first signal parameter is generated as a function of time and frequency by means of the first signal processing arrangement, associated with the first series circuit, in response to the output signal, after which the first signal parameter is compressed by means of the first compressing arrangement associated with the first series circuit. In this connection, intermediate operational processing of said first signal parameter should not be ruled out at all. The second signal parameter is compressed by means of the second compressing arrangement associated with the second series circuit in response to the reference signal. In this connection, too, further operational processing of said second signal parameter should not be ruled out at all. Of both compressed signal parameters the differential signal is determined by means of the differential arrangement associated with the combining circuit, after which the quality signal is generated by integrating the differential signal with respect to time and frequency by means of the integrating arrangement associated with the combining circuit. This known device is improved by adding the scaling circuit to it. Due to this scaling circuit, the objective quality signal to be assessed by means of said improved device and a subjective quality signal to be assessed by human observers have a good correlation.
However, such a device has, inter alia, the disadvantage that in case the signal processing circuit comprises a radio link, the objective quality signal to be assessed by means of said device and a subjective quality signal to be assessed by human observers have a poor correlation.
The object of the invention is, inter alia, to provide a device of the type mentioned in the preamble, the objective quality signal to be assessed by means of said device and a subjective quality signal to be assessed by human observers having a better correlation.
For this purpose, the device according to the invention has the characteristic that the device comprises a discounting arrangement situated between the comparing arrangement and the integrating arrangement for discounting the comparison at the integrating arrangement.
As a result of providing the device with the discounting arrangement, in particular large amplitude differences present between both series circuit signals can be discounted at the integrating arrangement. Due to said discounting, a good correlation is obtained between the objective quality signal to be assessed by means of said device and a subjective quality signal to be assessed by human observers, even when the signal of which the quality has to be determined is transported via a radio link.
The invention is based, inter alia, on the insight that the poor correlation between objective quality signals to be assessed by means of known devices and subjective quality signals to be assessed by human observers could also be the consequence, inter alia, of the fact that in particular large amplitude differences present between both series circuit signals imply a bad quality.
The problem of the poor correlation is thus solved by using the discounting arrangement coupled to the scaling circuit.
It should be noted that the device of the present invention will also improve the correlation in case the signal processing circuit comprises an ATM link and in case the signal processing circuit generates signals which differ a lot from signals originating from or belonging to the reference signal.
A first embodiment of the device according to the invention has the characteristic that the scaling circuit is provided with
a scaling unit comprising
an input coupled to an output of the first signal processing arrangement,
an output coupled to an input of the first compressing arrangement, and
a control input coupled to an output of the comparing arrangement for scaling the first series circuit signal in response to the comparison.
As a result of providing the scaling circuit with the scaling unit for scaling the first series circuit signal, the scaling circuit functions best. As a result, the correlation is improved still further.
A second embodiment of the device according to the invention has the characteristic that the integrating arrangement comprises
an integrator for integrating the differential signal with respect to frequency, and
a time averaging arrangement for generating the quality signal by integrating the integrated differential signal with respect to time, the discounting arrangement comprising
a processing arrangement for processing a comparison signal originating from the comparing arrangement, and
a multiplying arrangement comprising
a first input coupled to an output of the processing arrangement,
a second input coupled to an output of the integrator, and
an output coupled to an input of the time-averaging arrangement.
By providing the discounting arrangement with the processing arrangement and with the multiplying arrangement, the latter being situated between the integrator and the time-averaging arrangement, the discounting arrangement is coupled to the integrating arrangement in a most efficient way.
A third embodiment of the device according to the invention has the characteristic that the processing arrangement raises the comparison signal to the power p, where 0 less than p less than 1.
In this connection, large amplitude differences are rescaled in dependence of a relationship between both series circuit signals.
A fourth embodiment of the device according to the invention.has the characteristic that the second series circuit is furthermore provided with
a second signal processing arrangement, coupled to the second input, for generating a second signal parameter as a function of both time and frequency, the second compressing arrangement being coupled to the second signal processing arrangement in order to compress the second signal parameter.
The invention furthermore relates to a method for determining the quality of an output signal to be generated by a signal processing circuit with respect to a reference signal, which method comprises the following steps of
generating a first signal parameter as a function of time and frequency in response to the output signal,
integrating, with respect to frequency, a first signal parameter and a second signal parameter,
comparing the integrated first and second signal parameters,
scaling at least one of the first and second signal parameters in response to a comparison signal,
compressing a first signal parameter and a second signal parameter,
determining a differential signal on the basis of the compressed signal parameters, and
generating a quality signal by integrating the differential signal with respect to frequency and time.
The method according to the invention has the characteristic that the method furthermore comprises the step of
discounting the comparison signal at the integrating of the differential signal with respect to frequency and time.
A first embodiment of the method according to the invention has the characteristic that the method comprises the step of
scaling the first signal parameter in response to the comparison.
A second embodiment of the method according to the invention has the characteristic that the method comprises the following steps of
processing the comparison signal,
integrating the differential signal with respect to frequency,
multiplying the integrated differential signal with the processed comparison signal for generating a resulting signal, and
integrating the resulting signal with respect to time.
A third embodiment of the method according to the invention has the characteristic that the step of processing the comparison signal comprises the step of raising the comparison signal to the power p, where 0 less than p less than 1.
A fourth embodiment of the method according to the invention has the characteristic that the method comprises the step of
generating the second signal parameter as a function of both time and frequency in response to the reference signal.
WO 96/28953
WO 96/28950
WO 96/28952
J. Audio Eng. Soc., Vol. 40, No. 12, December 1992, in particular, xe2x80x9cA Perceptual Audio Quality Measure Based on a Psychoacoustic Sound Representationxe2x80x9d by John G. Beerends and Jan A. Stemerdink, pages 963-978
xe2x80x9cModelling a Cognitive Aspect in the Measurement of the Quality of Music Codecsxe2x80x9d, by John G. Beerends and Jan A. Stemerdink, presented at the 96th Convention Feb. 26-Mar. 1, 1994, Amsterdam
All the references including the literature cited in these references are deemed to be incorporated in this patent application.